兰州大学的中子发生器研制及应用展望

1988年兰州大学成功研制了3×10¹² s^-1的ZF-300强流中子发生器，主要用于核数据测量、材料辐照损伤等研究。为进一步开展活化法中子核数据测量、裂变物理等研究，兰州大学启动了基于倍压加速器的ZF-400强流中子发生器研制工程，该中子发生器的设计指标为D束流能量400 keV、D束流强度大于30 mA、D-D中子产额大于5×10¹⁰ s^-1，D-T中子产额大于5×10¹² s^-1。在裂变物理研究方面，已成功发展了描述裂变核断点裂变势的势驱动模型（potential-driving model），并开展了中子诱发典型锕系核素裂变发射中子前裂变产物的质量分布计算研究；将potential-driving model植入Geant4程序，发展了用于裂变发射中子后裂变产物质量分布、动能分布、裂变中子能谱等模拟的蒙特卡罗方法，并开展了可靠性评估研究；研制了一套用于裂变产物实验测量的双屏栅电离室（TFGIC）,并完成了初步实验测试。在中子应用技术方面，为满足小型化中子应用技术系统的研发需求，兰州大学成功研制了长度984 mm、直径234 mm的紧凑型中子发生器，通过在引出加速电极和靶之间加电阻的方式产生偏置电场，实现对靶上二次电子的抑制。在自注入靶条件和150 keV氘束流能量下，D-D中子产额可大于5×10⁸ s^-1，该中子发生器已具备产生D-T中子产额大于10¹⁰ s^-1量级的潜力。完成了基于紧凑型D-T中子发生器的快中子准直屏蔽体的设计，并研发了基于微通道板的快中子成像探测器，初步D-T快中成像测试显示，图像空间分辨率约为500 μm。开展了基于紧凑型D-D中子发生器的核燃料棒²³⁵U富集度及均匀性检测系统研发，仿真研究表明，在D-D中子产额5×10⁸ s^-1条件下，对核燃料棒中10%范围内的²³⁵U富集度相对变化的检测置信度可达到99%。

Development and Application of Neutron Generator at Lanzhou University

In 1988, a 3×10¹² s^-1 neutron generator named ZF-300 was built at Lanzhou University. The neutron source was used in the programs involving basic nuclear data measurements, irradiation effect researches of materials. Recently, a new intense neutron generator named ZF-400, is being developed for the purposes of fast neutron physics research, such as fast neutron nuclear data measurement by activation method and fission physics. The Cockcroft-Walton accelerator was designed to accelerate the D⁺ beam of 30 mA to the energy of 400 keV. The designed neutron yields of ZF-400 neutron generator were greater than 5×10¹⁰ s^-1 for D-D and 5×10¹² s^-1 for D-T, respectively. In the field of fission physics, a potential-driving model by uniting the empirical asymmetric fission potential and the empirical symmetric fission potential was successfully developed to precisely calculate the pre-neutron-emission mass distributions for neutron-induced actinide nuclei fission. A Monte-Carlo method based on the potential-driving model and Geant4 code was also developed to simulate the fission-fragment yield distribution, kinetic energy distribution and fission neutron spectrum. A twin frisch-grid ionization chamber (TFGIC) detector for the measurement of fission products was also designed and tested. In the field of neutron application technology, in order to meet the development requirements of neutron application technology system, a compact neutron generator with a length of 984 mm and a diameter of 234 mm was successfully developed at Lanzhou University. A bias voltage between the target and the extraction accelerating electrode was produced by a resistance to suppress the secondary electron from the target. D-D neutron yield of the compact neutron generator could be greater than 5×10⁸ s^-1 under a pure molybdenum as the drive-in target and the beam energy of 150 keV. The compact neutron generator has the potential to produce D-T neutrons with a yield of more than 10¹⁰ s^-1. A beam-shaping-assembly (BSA) based on a compact D-T neutron generator was designed for fast neutron radiography, and a fast neutron imaging detector based on micro-channel plates was also developed. Preliminary fast neutron imaging test using D-T neutron generator shows that the spatial resolution of the image is about 500 μm. A detection system to measure ²³⁵U enrichment uniformity in nuclear fuel rods based on a compact D-D neutron generator was also designed. Simulation results show that the confidence probability can reach 99% for a relative ²³⁵U enrichment deviation of 10% under a D-D neutron yield of 5×10⁸ s^-1.